Luminescence control of Stomiidae photophores

The first evidence of intrinsic epidermal bioluminescence within ray‐finned fishes in the linebelly swallower Pseudoscopelus sagamianus (Chiasmodontidae)

“…The purpose of this study was to determine the structure of the bioluminescent organs in Pseudoscopelus spp. In particular, we seek to test the hypothesis that they produce light intrinsically using tissues in the dermis as in those other taxa with serial photophores that have been closely studied anatomically (Lawry, ; Mallefet et al ., ; Nichol, ). We used preserved museum specimens and did not collect or work with live animals.…”

“…Epidermal involvement in photophore structure is more typical of bacterial bioluminescent organs where bacteria must be acquired from the environment, but in these cases the epidermal epithelium forms a chamber to house obvious groups of bacteria (Chakrabarty et al ., ; Ghedotti et al ., ; Munk, ; Somiya, ). Although serial photophores in other taxa may also have a developmental origin from generalised ectoderm like the epidermis, in the adult these structures are restricted to the dermis (Lawry, ; Mallefet et al ., ; Nichol, ). This study provides evidence of a bioluminescent photophore that is probably intrinsic in a continuous epidermal tissue in ray‐finned fishes, it expands the range of tissues that probably function in intrinsic bioluminescence and it increases the number of inferred independent acquisitions of intrinsic bioluminescence to 11 (Davis et al ., ).…”

“…Cases where the bioluminescent bacteria are primarily intracellular are not known in fishes (Labella et al ., ). Intrinsic bioluminescence evolved in a more diverse range of tissues of origin, including muscle (Johnston & Herring, ; Merrett et al ., ), the hepatopancreas (Ghedotti et al ., ), the intestine (Herring, ) and the dermis (Hansen & Herring, ; Lawry, ; Mallefet et al ., ; Nichol, , ; Poulsen, ). In a few clades of fishes, the anatomical basis of their bioluminescence has not been established (Davis et al ., ).…”

“…The only dermal component appears to be the dark chromatophores that form the pigmented cup deep to the rest of the photophore in a capillary‐rich region of the superficial dermis. If photophores in P. sagamianus are structured analogously to the photophores in other taxonomic groups with serial photophores (Lawry, ; Mallefet et al ., ; Nichol, ), then, from deep to superficial, the dermal chromatophores form the pigment cup or reflector, followed by epidermal photocytes, filter and lens.…”

“…This epidermal continuity was contrary to our initial expectation that the photophores would be composed primarily of structures in the dermis. The photophores exhibit a structure typical of many intrinsically bioluminescent taxa with overlying tissues serving as a filter or lens (Ghedotti et al ., ; Hansen & Herring, ; Lawry, ; Mallefet et al ., ; Nichol, , ; Poulsen, ). The photophores also lack the obvious bacteria‐containing chambers present in all other known bacterially bioluminescent fish taxa (Bassot, ; Chakrabarty et al ., ; Dunlap & Nakamura, ; Ghedotti et al ., ; Haneda, ; Munk, ; Okada, ; Poulsen et al ., ; Somiya, ) (Figure d,f).…”